Does the Dielectric-Dielectric Interface Affect the Positron Diffusion Current?

The angular correlations of annihilation radiation have been measured for NaI, NaF and (NaI)_{0.65}(NaF)_{0.35} alloy. The angular correlations of annihilation radiation for the alloy appeared to be more similar to the one for NaI than it should be expected from the content of NaI in the alloy. The result can be easily explained by assuming that NaI/NaF interface acts directionally on positron diffusion movement.